This study focuses on the role of early childhood inhibition in the development of pathological risk indicators in children of families with and without parental depression. Patterns of child behavior in the face of the unfamiliar (persons, places), such as behaviors expressing inhibited exploratory activity and social withdrawal are observed at 2 to 3 years of age and again, at 5 to 6 years of age in semi-naturalistic but standard settings, which represent varied contexts of unfamiliarity. Preliminary analyses of the data from the earlier period of measurement (2-3 years of age) revealed that four reliable dimensions of response styles could be empirically derived from our observation coding system, which meaningfully distinguish groups of children in our sample at this very young age. Comparisons of these four dimensions of early behavioral inhibition across maternal diagnostic groups of normal, major depressive and bipolar indicate that the young children of the major depressive mothers in our sample typically exhibit the most inhibited forms of these response characteristics. The children of the Bipolar mothers typically exhibit the most active and independent forms of response when the situation is that of an unfamiliar environment. However, in the situation of an unfamiliar person, the children of the Bipolar mothers, as a group, exhibit very divergent forms of response to this kind of environmental challenge, scoring at both the inhibited and uninhibited polar extremes of the response scales. Longitudinal data are being analyzed to examine the direct and indirect associations of these early response characteristics of inhibition with later manifestations of disordered or healthy behavior at 5-6 years.